You may receive this dialogue if you’re using a fresh install of SSMS, or after an upgrade. It simply means your environment hasn’t been configured to allow certain changes which require the dropping, and re-creation, of a table.
Such actions include:
Adding a new column anywhere other than the end of a table
Deleting a column
Updating column configuration, such as Allow Nulls or the Data Type
Changing the column order
You can modify your environmental settings to allow for these actions form the Tools menu. Click Options, expand Designers, and then click Table and Database Designers. Un-tick Prevent saving changes that require the table to be re-created and click OK.